Imagine an America that was a true Empire, in the Roman fashion. An America with the additional 51st state of Germany, 52nd of South Korea, 53rd of Cuba, 54th of the Philippines and 55th of Japan? Hell, why stop there? An American claim to France would have been just as strong as a Roman claim to Egypt (namely, America claims it, who disagrees?), let's seize Canada, stop paying for oil to the House of Saud, figure out what we're going to do with our territories of Iraq, Kuwait and Afghanistan. America isn't a true empire, but it has some flavors of one.

The U.S. is a weird sort of quasi-empire with military outposts and large economic interests all over the world, but in territories that aren't their own and with the notion that the countries we inhabit are not part of the U.S. in any way shape or form. Sort of like vassal states, but without all the "pay us your tribute or we'll invade and burn your cities down" that modern America is terribly uncomfortable with.

It's an interesting academic exercise to pick apart where the U.S. is and isn't like an Empire because it's not that simple.